Last wek, a Mexican carrier executive of Telcel announced that the "iPhone 4 will go on sale on Friday Aug 27, and that a hardware revision will be coming at the end of September, without reception issues." The executive explained that Apple will be shipping a hardware revision for iPhone 4 at the end of September, the same time the company plans to stop giving out free cases. Telcel said that the updated iPhone 4 hardware will be available on Sep 30, 2010.
It's not uncommon for a manufacturer to release a hardware refresh on a faulty product partway through its lifecycle, like when Apple released an updated bootrom for the iPhone 3GS in mid-Sep 2009, just months after it was originally released. The updated bootrom made it harder for hackers to jailbreak and unlock the phone.